The present invention relates to thermal energy collecting systems, and in particular, to heating a molten storage medium used in thermal energy collecting systems.
Throughout the world there is an increasing demand for energy, which is typically provided by fossil fuels such as petroleum and coal. Additionally, due to scarcity and adverse environmental effects of fossil fuels, cleaner, renewable energy sources are becoming more desirable. As technology advances, alternative fuel sources are becoming practical to replace, or at least augment, conventional power plants to meet worldwide energy demand in a clean manner. In particular, solar energy is freely available and is becoming more feasible, especially in the form of concentrated solar power, which allows for energy storage and can be scaled for commercial production.
Concentrated solar power generation systems typically comprise solar collectors that focus solar rays onto a heat transfer medium such as a molten salt. For example, solar power towers use an array of thousands of heliostats to concentrate energy on an elevated central receiver through which molten salt flows inside of numerous pipes. In solar trough systems, molten salt flows through extended lengths of piping which are shrouded by solar collecting troughs that concentrate energy along lengths of the pipes. Heat from the solar energy is transferred to the molten salt and then through a heat exchanger to another medium, such as air or water, which is then used to generate mechanical energy that is ultimately converted to electrical power. Molten salt efficiently stores heat from the solar energy for extended periods of time such that electrical power can be generated at night or during other periods of low solar collection.
Molten salts can solidify if cooled below a certain temperature. Consequently, pipes and tanks holding the molten salt are typically wrapped in electrical trace heating elements (electrical resistance wires). Electrical trace heating can, however, be relatively expensive, increasing total cost of power production. Moreover, electrical trace heating can be prone to failure, causing the entire solar power generation system to require shut-down for maintenance. There is, therefore, a need for improved heating of pipes and tanks for the heat transfer medium in a solar power generation system.